ZnO nanopencils: Efficient field emitters

ZnO nanopencils were synthesized on a silicon wafer without catalysts at a low temperature of 550 ° C through a simple two-step pressure controlled thermal evaporation. Penholders were well-hexagonal faceted and the diameter of pen tips on the nanopencils was in the range of 20-30 nm. High-resolution transmission electron microscopy shows that the nanopencils were single crystals growing along the [0001] direction and the pen tips subtend a small angle with multiple surface perturbations. Field-emission measurements on the nanopencils show a low turn-on field of 3.7 Vμm at a current density of 10 μA cm2. The emission current density reached 1.3 mA cm2 at an applied field of 4.6 Vμm. The emission at the low field is attributed to the sharp tip and surface perturbations on the nanopencils.